synthesis,characterization,andevaluationofboron-doped...

Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2012, Article ID 598713, 4 pagesdoi:10.1155/2012/598713

Research Article

Synthesis, Characterization, and Evaluation of Boron-DopedIron Oxides for the Photocatalytic Degradation of Atrazine underVisible Light

Shan Hu, Guanglong Liu, Duanwei Zhu, Chao Chen, and Shuijiao Liao

Laboratory of Plant Nutrition and Ecological Environment Research, Centre for Microelement Research of Huazhong AgriculturalUniversity, Key Laboratory of Subtropical Agriculture and Environment, Ministry of Agriculture, Wuhan 430070, China

Correspondence should be addressed to Duanwei Zhu, [email protected]

Received 23 July 2011; Accepted 15 September 2011

Academic Editor: Shifu Chen

Copyright © 2012 Shan Hu et al. This is an open access article distributed under the Creative Commons Attribution License, whichpermits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Photocatalytic degradation of atrazine by boron-doped iron oxides under visible light irradiation was investigated. In this work,boron-doped goethite and hematite were successfully prepared by sol-gel method with trimethylborate as boron precursor. Thepowders were characterized by XRD, UV-vis diffuse reflectance spectra, and porosimetry analysis. The results showed that borondoping could influence the crystal structure, enlarge the BET surface area, improve light absorption ability, and narrow theirband-gap energy. The photocatalytic activity of B-doped iron oxides was evaluated in the degradation of atrazine under the visiblelight irradiation, and B-doped iron oxides showed higher atrazine degradation rate than that of pristine iron oxides. Particularly,B-doped goethite exhibited better photocatalytic activity than B-doped hematite.

1. Introduction

Atrazine, 2-chloro-4-ethylamino-6-isopropylamino-1,3,5-tri-azine, has been widely used in the fields of corn, sorghum,orchard, and forest, controlling broad-leaf and grassy weeds[1]. However, due to the toxicity to aquatic organisms andmammals, high mobility, low-sorption affinity, and slowbiodegradability [2, 3], atrazine has been banned by manyEuropean countries. It is frequently detected in ground waterand surface water [4] and seriously influenced water quality.Therefore, many ways have been found to resolve atrazinecontamination, such as advanced oxidation processes [5],microorganism removal [6], and microwave irradiation [7].

It has been reported that photocatalysis is effective way inthe degradation of organic pollutants. TiO2 is considered tobe the most promising photocatalyst due to its nontoxicity,chemical inertness, and high reactivity. Parra found thatboth suspended and supported TiO2 could destroy atrazinealthough atrazine could not be completely mineralized[8]. However, the widespread technological use of TiO2 isimpaired by its wide-band gap (3.2 eV), which can onlybe activated under UV light. Iron oxides especially goethite

and hematite have been studied as photocatalysts in recentyears because their lower band gap (2.2 eV), and nonmentaldoping could improve reactivity of photocatalysts [9, 10].It is reported that PE films with boron-doped goethite hashigher photo-induced degradation than pure PE films underthe UV irradiation [11]. In this paper, B-doped goethiteand hematite were prepared as photocatalysts, and enhance-ment of photocatalytic activity of atrazine degradation wasobserved under visible light irradiation.

2. Experimental

2.1. Materials. Fe(NO3)3, (CH3O)3B, KOH, methanol weresupplied from Guoyao Chemical Co. (Shanghai, China)and atrazine was supplied from the Laboratories of Dr.Ehrenstorfer (Germany). All chemicals were used withoutfurther purification, and deionized water was used in all theexperiments.

2.2. Preparation of Photocatalysts and Characterization. Theoriginal goethite (G-S-B0%) was prepared according to the

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ty

2-θ

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Figure 1: X-ray diffraction patterns of goethite and B-dopedgoethite.

method of Atkinson et al. [12], and the preparation of B-doped goethite photocatalysts was the same as the methodof Liao et al. [13], while the atomic weight ratio of B toFe was 2% (G-S-B2%). Goethite and B-doped goethite werecalcined at 400◦C for 2 h to obtain the original hematite (H-S-B0%) and B-doped hematite (H-S-B2%), respectively.

The Brunauer-Emmett-Teller surface areas of the pow-der samples were determined by nitrogen adsorption-desorption isotherm measurements on a ST-08 nitrogenadsorption apparatus. The X-ray powder diffraction patternwas obtained with a Brook D8 diffractometer using Fe Kαradiation with an accelerating voltage of 40 kV and currentof 20 mA. The UV-vis diffuse reflectance spectra of differentiron oxides in the 190–900 nm were recorded using anAmerican Lambda35 UV-vis spectrophotometer.

2.3. Photocatalytic Evaluation with Atrazine under VisibleLight. The photocatalytic activities of pure and B-dopediron oxides nanoparticles were evaluated by the degradationof atrazine under visible light irradiation at a constanttemperature (25◦C). 25 mL 10 mg·L−1 atrazine solution wasput in 50 mL of centrifugal test tube with 100 mg differentphotocatalysts, and then all tubes were placed in a constanttemperature shaking incubator at a speed of 190 r·min−1.A 250 W metal halide lamp (λ > 385 nm, JLZ250KN,Shanghai Yaming Co.) was put above all tubes as the visiblelight irradiation with a distance of 80 cm. At differenttime intervals during the irradiation, samples were col-lected, filtered, and finally analyzed by HPLC (Agilent1100).Atrazine was detected at 222 nm and the mobile phasewas methanol/water mixture (80 : 20, v/v) at a flow rate of1.0 mL·min−1 using C18 column (4.6 mm × 150 mm).

3. Results and Discussion

3.1. Crystal Structure. XRD was carried out to investigatethe changes of goethite and hematite phase structure after

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Figure 2: X-ray diffraction patterns of hematite and B-dopedhematite.

300 400 500 600 700 800 9005

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40R

(%)

Wavelength (nm)

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Figure 3: UV-visible light reflection spectrum of goethite and B-doped goethite.

boron doping and heat treatment. Figure 1 shows the X-ray diffraction patterns of goethite and B-doped goethite.Compared with G-S-B0%, there is no significant new peakappearing in G-S-B2%, but the intensity of some peaksbecome weaker or stronger. Maybe the content of boron istoo small to make perceptible crystal change of goethite’sstructure by X-ray diffraction. But boron does make aninfluence in the crystal structure of goethite. Figure 2 showsthe crystal form change of common hematite and hematitewith 2% boron doping. It seems that H-S-B0% and H-S-B2% have the same peaks. Perhaps the high calcinationtemperature destroyed the changes of doping.

3.2. UV-vis Diffuse Reflectance Spectra. Figure 3 illus-trates the UV-vis light reflection spectrum of goethite and

International Journal of Photoenergy 3

300 400 500 600 700 800 9005

10

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R(%

)

Wavelength (nm)

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Figure 4: UV-visible light reflection spectrum of hematite and B-doped hematite.

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Ct/C

0(%

)

Irradiation time (h)

17

G-S-B0%G-S-B2%

Figure 5: Atrazine degradation in present of goethite and B-dopedgoethite under visible light.

Table 1: The properties of different B-doped goethite and hematite.

Samples BET(m2/g) Band-gap energy (eV)

G-S-B0% 60.24 2.06

G-S-B2% 91.46 1.97

H-S-B0% 56.26 1.69

H-S-B2% 71.48 1.68

boron-doped goethite. In the UV part, G-S-B0% and G-S-B2% show the same reflection rate, while in the visiblepart, G-S-B2% shows stronger light absorption than G-S-B0%. The UV-vis light reflection spectra of undoped and2% boron-doped hematite were shown in Figure 4. H-S-B2% shows stronger absorption than H-S-B0% during the

H-S-B0%H-S-B2%

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Ct/C

0(%

)

Irradiation time (h)

Figure 6: Atrazine degradation in present of hematite and B-dopedhematite under visible light.

whole wavelength range. The band-gap energy of these fouriron oxides were estimated by Eg = 1240/λonset [14] andpresented in Table 1. It is inferred that boron doping maynarrow the band-gap energy of iron oxides and improve theirlight absorption ability.

3.3. BET Surface Area. Table 1 lists the BET surface areas offour iron oxides. G-S-B2% exhibits higher BET surface areathan that of G-S-B0% (34.13%), and the BET surface areaof H-S-B2% is also larger than that of H-S-B0%(21.29%).These results confirm that boron doping can efficientlyinhibit the crystal size growth and increase the surface areaof goethite and hematite.

3.4. Visible Light Photocatalysis of Atrazine. To examine thephotocatalytic activity of B-doped iron oxides, atrazine waschosen as target contaminant. And the degradation rate ofatrazine through the reaction time in present of these fouriron oxides under visible light was displayed in Figures 5and 6. The photocatalytic degradation of atrazine followedthe first-order reaction kinetics under visible light accordingto lnCt = lnC0 − kt, where C0 stands for the initialconcentration of atrazine and Ct is the concentration ofatrazine at t time. All the numbers were collected in Table 2.The results clearly indicated that G-S-B2% and H-S-B2%revealed a substantially enhanced activity for degradationof atrazine, as compared to undoped G-S-B0% and H-S-B0% under visible light irradiation. The first-order kineticsconstants (k) for atrazine degradation by G-S-B0%, G-S-B2%, H-S-B0%, and H-S-B2% were 0.0295 h−1 (R =0.9774), 0.0301 h−1 (R = 0.9857), 0.0199 h−1 (R = 0.9757),and 0.0202 h−1 (R = 0.9932), respectively, and the half lives(t1/2) of atrazine degraded by them were 23.49 h, 23.02 h,34.82 h, and 34.31 h, respectively. It was confirmed thatboron doping could show good optical activity and goethite

4 International Journal of Photoenergy

Table 2: Degradation kinetic results of atrazine under visible light irradiation with different iron oxides.

Experiments conditions lnCt = lnC0 − kt R k (h−1) t1/2 (h)

G-S-B0% lnCt = 0.8261− 0.0295t 0.9774 0.0295 23.49

G-S-B2% lnCt = 0.7895− 0.0301t 0.9857 0.0301 23.02

H-S-B0% lnCt = 0.8240− 0.0199t 0.9757 0.0199 34.82

H-S-B2% lnCt = 0.7983− 0.0202t 0.9932 0.0202 34.31

had better catalytic activity than hematite under visible lightirradiation.

4. Conclusion

The degradation of atrazine by using visible light-activatedB-doped iron oxide as photocatalyst is demonstrated inthis paper. Goethite, hematite, and B-doped goethite andhematite were successfully synthesized by a novel modifiedsol-gel method. Although there is no significant differentin XRD results between pure iron oxide and B-doped ironoxide, however, the BET surface area and UV-vis spectraindicate that boron doping greatly influenced the propertiesof iron oxide. G-S-B2% and H-S-B2% exhibited enhancedvisible light photocatalytic activity in degradation of atrazinecompared with G-S-B0% and H-S-B0%, which maybe dueto the stronger light adsorption and boron-doped goethiteexhibited better photocatalytic activity than boron-dopedhematite.

Acknowledgments

This work was supported jointly by the National NaturalScience Foundation of China (40973056; 40371064) andSpecialized Research Fund for the Doctoral Program ofHigher Education (SRFDP) of the Ministry of Education ofPRC (20100146110020).

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